MCP9600

Contributed by Matteo Golin.

The MCP9600 is a thermocouple EMF to temperature converter made by Microchip. It is also sold as a breakout board module by Adafruit.

Application Programming Interface

The header file for the MCP9600 driver interface can be included using:

#include <nuttx/sensors/mcp9600.h>

The MCP9600 registration function allows the driver to be registered as a UORB sensor.

The MCP9600 measures three types of temperature:

• Hot junction temperature

• Cold junction temperature

• Temperature delta

Registering this sensor will create three UORB temperature topics, each with their own unique device number. You must specify the unique device numbers for each topic in the registration function:

/* Registers sensor_temp1, sensor_temp2 and sensor_temp 3, where 1 is the
 * hot junction topic, 2 is the cold junction topic and 3 is the delta
 */

int err;
err = mcp9600_register(i2c_master, 0x60, 1, 2, 3);
if (err < 0) {
  syslog(LOG_ERR, "Could not register MCP9600: %d\n", err);
}

This sensor offers some additional control commands for features that are not accessible with the standard UORB interface.

• SNIOC_SET_THERMO

• SNIOC_WHO_AM_I

• SNIOC_READ_RAW_DATA

• SNIOC_CHECK_STATUS_REG

• SNIOC_CONFIGURE

• SNIOC_WRITECONF

SNIOC_SET_THERMO

This command configures the thermocouple type of the MCP9600. The device supports the following thermocouple types:

• K

• J

• T

• N

• E

• S

• B

• R

int err;
err = orb_ioctl(sensor, SNIOC_SET_THERMO, SENSOR_THERMO_TYPE_J);
if (err < 0) {
  syslog(LOG_ERR, "Failed to set thermocouple type: %d\n", err);
}

SNIOC_WHO_AM_I

This command reads the device ID register of the MCP9600 sensor. The device ID, major and minor revision numbers are returned in the argument, which must be of type struct mcp9600_devinfo_s *.

struct mcp9600_devinfo_s devinfo;
err = orb_ioctl(sensor, SNIOC_WHO_AM_I, &devinfo);

uint8_t revision_minor = MCP9600_REV_MINOR(devinfo.revision);
uint8_t revision_major = MCP9600_REV_MAJOR(devinfo.revision);

SNIOC_READ_RAW_DATA

This command allows the caller to read the raw data returned from the sensor’s ADC.

The argument to this command must be an int32_t pointer. The raw data will be returned here. The process to convert the raw ADC data depends on the configured resolution; consult the data sheet.

int32_t raw;
err = orb_ioctl(sensor, SNIOC_READ_RAW_DATA, &raw);

SNIOC_CHECK_STATUS_REG

This command lets you check the status register of the device. The argument to this command must be a pointer to type struct mcp9600_status_s.

struct mcp9600_status_s status;
err = orb_ioctl(sensor, SNIOC_CHECK_STATUS_REG, &status);

SNIOC_CONFIGURE

This command lets you configure the MCP9600’s operation, including thermocouple type, operating mode, ADC resolution, etc.

The argument to this command must be a pointer to type struct mcp9600_devconf_s.

struct mcp9600_devconf_s conf = {
  .thermo_type = MCP9600_THERMO_TYPE_K,
  .resolution = MCP9600_ADC_RES_18,
  /* More fields ... */
};
err = orb_ioctl(sensor, SNIOC_CONFIGURE, &conf);

SNIOC_WRITECONF

This command lets you configure the MCP9600’s alerts on a per-alert basis.

The argument to this command must be a pointer to type struct mcp9600_alertconf_s.

struct mcp9600_alertconf_s conf = {
  .alert = MCP9600_ALERT1,
  .enable = true,
  .limit = 40 / 0.25,
  /* More fields ... */
};
err = orb_ioctl(sensor, SNIOC_WRITECONF, &conf);